The present invention relates to polyarylene copolymers. More particularly, the invention relates to a polyarylene copolymers useful as a proton-conductive membrane utilizable in applications such as electrolytes for primary batteries, electrolytes for secondary batteries, solid polymer electrolytes for fuel cells, display elements, various sensors, signal-transmitting media, solid capacitors, and ion-exchange membranes. The invention further relates to a proton-conductive membrane formed from the copolymer.
Electrolytes are usually used as (aqueous) solutions in many cases. In recent years, however, there is a growing tendency to replace such aqueous soluble-form electrolytes with solid electrolytes. The first reason for this is the easiness of processing in applications of solid electrolytes to, e.g., the electrical/electronic materials mentioned above. The second reason is the trend toward reduction in weight, thickness, length and size, and toward energy saving.
Conventional proton-conductive materials include both inorganic materials and organic materials. Examples of the inorganic materials include uranyl phosphates which form hydrate. However, these inorganic compounds are insufficient in interfacial contact to pose many problems concerning the formation of a conductive layer on a substrate or electrode.
On the other hand, examples of the organic compounds include organic polymers such as polymers belonging to the so-called cation-exchange resins, e.g., sulfonated vinyl polymers such as sulfonated polystyrene (co)polymers with perfluoroalkylsulfonic acid represented by Nafion (manufactured by E.I. du Pont de Nemours and Co., Inc.), and perfluoroalkylcarboxylic acid polymers, and polymers prepared with incorporating sulfonic acid groups or phosphonic acid groups into heat-resistant polymers such as polybenzimidazole and poly(ether-ether-ketone)s [see Polymer Preprints, Japan, Vol.42, No.7, pp.2490-2492 (1993); Polymer Preprints, Japan, Vol.43, No.3, pp.735-736 (1994); and Polymer Preprints, Japan, Vol.42, No.3, p.730 (1993)].
Although these organic polymers are usually used in the form of a membrane, a conductive membrane thereof can be bonded to an electrode while taking advantage of the solvent-soluble or thermoplasticity thereof. However, many of those organic polymers have the following problems besides being still insufficient in proton conductivity. The organic polymers deteriorate in mechanical properties and durability or in proton conductivity at elevated temperatures (100xc2x0 C. or higher), and the proton conductivity thereof highly depends on humidity conditions. Adhesion to the electrode is not fully satisfactory. Furthermore, the conductive membrane swells excessively during operation due to the hydrophilic polymer structure, and this swelling leads to a decrease in strength properties or a deformation. Consequently, application of those organic polymers to the aforementioned electrical/electronic materials and the like pose various problems.
U.S. Pat. No. 5,403,675 proposes a solid polymer electrolyte comprising a sulfonated rigid polyphenylene. This polymer is produced from a polymer comprising a phenylene chain obtained by polymerizing an aromatic compound (the polymer structure is described in column 9 in the specification) by reacting the phenylene polymer as the main component with a sulfonating agent to incorporate sulfonic acid groups thereinto. However, the incorporation of a large amount of sulfonic acid groups results in a sulfonated polymer having considerably impaired mechanical strength properties although proton conductivity improves with the increasing amount of sulfonic acid groups incorporated. It is therefore necessary to regulate the concentration of sulfonic acid groups to a proper value which enables the sulfonated polymer to retain intact excellent mechanical properties and have proton conductivity. Virtually, however, sulfonation of this polymer is apt to proceed excessively and it is exceedingly difficult to properly regulate the amount of sulfonic groups incorporated.
The invention has been achieved in view of the conventional technical problems.
One object of the invention is to provide polyarylene copolymers which can be sulfonated while being easily regulated with respect to the upper limit of sulfonic acid group incorporation amount so as not to impair mechanical properties and thus gives a sulfonated polymer which has high proton conductivity in a wide temperature range, has excellent mechanical strength, is reduced in swelling in hot water, and gives a proton-conductive membrane having excellent durability.
Another object of the invention is to provide a proton-conductive membrane formed from the copolymer.
The invention provides polyarylene copolymers which comprise (A) aromatic compound units having a main chain containing one or more electron-withdrawing groups and one or more ether bonds therein (hereinafter referred to also as xe2x80x9cunits (A)xe2x80x9d) and (B) aromatic compound units having a main chain containing no electron-withdrawing groups therein.
The electron-withdrawing groups preferably are divalent groups which are at least one member selected from the group consisting of xe2x80x94COxe2x80x94, xe2x80x94CONHxe2x80x94, xe2x80x94(CF2)pxe2x80x94 (wherein p is an integer of 1 to 10), xe2x80x94C(CF3)2xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94SOxe2x80x94, and xe2x80x94SO2xe2x80x94.
The polyarylene copolymer of the invention preferably are polyarylene copolymers having sulfonic acid groups (hereinafter referred to also as xe2x80x9csulfonic acid-containing copolymerxe2x80x9d or xe2x80x9csulfonated polymerxe2x80x9d).
The invention further provides proton-conductive membranes comprising the sulfonic acid-containing copolymers.